Certifying Twisted Pair Cabling
Twisted Pair Autotest Results
3-21
3
NEXT (Near-End Crosstalk)
NEXT results show the crosstalk attenuation between cable
pairs. NEXT is the difference in amplitude (in dB) between a
transmitted signal and the crosstalk received on other cable
pairs at the same end of the cabling. Higher NEXT values
correspond to better cabling performance.
Because of insertion loss, crosstalk signals occurring farther
from the signal source are weaker and cause less trouble
than crosstalk nearer the source (Figure 3-14). For this
reason, NEXT is measured from both ends of the cabling.
For NEXT failures, the tester's diagnostic screens (
J Fault
Info) may show more than one possible cause for the
failure. In this case, you can use the HDTDX analyzer results
to further diagnose the problem. See page 6-9 for details.
Figure 3-15 describes the NEXT plot.
Note
For ISO/IEC 11801:2002 and EN50173:2002
standards, NEXT is not evaluated where insertion
loss at the same frequency is less than 4 dB. If
insertion loss never exceeds 4 db, NEXT results are
marked with an i on the tester and an N/A in
LinkWare reports.
amd89f.eps
Figure 3-14. Near-End Crosstalk (NEXT)
Signal
source
Resulting
NEXT
Crosstalk near
the source
Crosstalk farther
from the source
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